by Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo
Figure 1: A picture obtained from observations of the large-scale structure of the universe. The many objects shown in yellow to red all represent galaxies located hundreds of millions of light years from Earth. Galaxies come in a wide variety of colors and shapes and are too numerous to count in the vastness of space. The spatial distribution and shape of these galaxies are not random, but indeed have “correlations” arising from the statistical properties of the primordial seed fluctuations as predicted by inflation. Credit: Subaru HSC
A team of researchers analyzed more than a million galaxies to explore the origin of current cosmic structures, as reported in a recent study published in Physical examination D as a suggestion from the editors.
Until today, precise observations and analyzes of the cosmic microwave background (CMB) and large-scale structure (LSS) have led to the establishment of the standard framework of the universe, called the ΛCDM model, in which cold dark matter (CDM) and dark energy (the cosmological constant, Λ) are significant features.
This model suggests that primordial fluctuations were generated at the beginning of the universe, or at the beginning of the universe, and acted as triggers, leading to the creation of all things in the universe, including stars, galaxies, clusters of galaxies, and their spatial distribution in space. . Although very small when generated, the fluctuations increase over time due to the force of gravitational attraction, eventually forming a dense region of dark matter, or a halo. Then different halos collided and merged repeatedly, leading to the formation of celestial objects such as galaxies.
Since the nature of the spatial distribution of galaxies is strongly influenced by the nature of the primordial fluctuations that created them, statistical analyzes of the distribution of galaxies have been actively carried out to explore by observation the nature of the primordial fluctuations. In addition to this, the spatial configuration of galaxy shapes spread over a large area of the universe also reflects the nature of the underlying primordial fluctuations (Figure 1).
However, conventional analysis of large-scale structures has focused only on the spatial distribution of galaxies as points. More recently, researchers have begun to study galaxy shapes because they not only provide additional information, but also offer a different perspective on the nature of primordial fluctuations (Figure 2).
Figure 2: Visualization of how “different” primordial fluctuations in the universe lead to a different spatial distribution of dark matter. The central figure (common to the upper and lower lines) shows the fluctuations of the reference Gaussian distribution. The color gradation (blue to yellow) corresponds to the fluctuation value at that location (low to high density regions). The left and right figures show fluctuations that deviate slightly from the Gaussian distribution or are non-Gaussian. The sign in parentheses indicates the sign of the deviation from Gaussianity, corresponding to a negative deviation (-) on the left and a positive deviation (+) on the right. The top row is an example of isotropic non-Gaussianity. Compared to the central Gaussian fluctuation, the left figure shows an increase in large negative regions (dark blue), while the right figure shows an increase in large positive regions (bright yellow). It is known that we can search for such isotropic non-Gaussianity using the spatial distribution of observed galaxies. The bottom panel shows an example of anisotropic non-Gaussianity. Compared to the isotropic case in the top panel, the overall brightness and darkness remain unchanged compared to the Gaussian fluctuation in the middle panel, but the shape of each region has changed. We can look for this “anisotropic” non-Gaussianity from the spatial configuration of galaxy shapes. Credit: Kurita ＆ Takada
A team of researchers, led by then-graduate student Toshiki Kurita at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) (currently a postdoctoral researcher at the Max Planck Institute for Astrophysics), and Professor Masahiro Takada from Kavli IPMU. developed a method for measuring the power spectrum of galaxy shapes, which extracts key statistical information from galaxy shape models by combining spectroscopic data of the spatial distribution of galaxies and imaging data of individual galaxy shapes.
Researchers simultaneously analyzed the spatial distribution and shape of approximately 1 million galaxies from the Sloan Digital Sky Survey (SDSS), the world’s largest galaxy survey to date.
As a result, they managed to constrain the statistical properties of the primordial fluctuations that seeded the formation of the structure of the entire universe.
They discovered a statistically significant alignment of the orientations of the shapes of two galaxies more than 100 million light years apart (Figure 3). Their results showed that there are correlations between distant galaxies whose formation processes are apparently independent and not causally related.
Figure 3: The blue dots and error bars are the power spectrum values of the galaxy shape. The vertical axis corresponds to the strength of correlation between two galaxy shapes, that is, the alignment of the orientations of the galaxy shapes. The horizontal axis represents the distance between two galaxies, with the left (right) axis representing the correlation between the more distant (closer) galaxies. Gray dots indicate apparent non-physical correlations. The fact that this value is zero within the error, as expected, confirms that the blue points measured are indeed signals of astrophysical origin. The black curve is the theoretical curve of the most standard inflationary model, and it turns out to be in good agreement with the actual data points. Credit: Kurita & Takada
“In this research, we were able to place constraints on the properties of primordial fluctuations through the statistical analysis of the “shapes” of many galaxies obtained from large-scale structure data. There are few precedents for research using shapes of galaxies to explore the physics of the early universe and the research process, from the construction of the idea and the development of analysis methods to the actual analysis of the data, was a series of tests and of errors.
“For this reason, I faced many challenges. But I am happy that I was able to overcome them during my doctoral program. I believe that this achievement will be the first step to open a new field of research in cosmology using the shapes of galaxies.” Kurita said.
Furthermore, a detailed study of these correlations confirmed that they are consistent with the correlations predicted by inflation and do not exhibit a non-Gaussian characteristic of the primordial fluctuation.
“This research is the result of Toshiki’s doctoral thesis. It is a wonderful research achievement in which we developed a method to validate a cosmological model using the shapes and distributions of galaxies, applied it to data, then tested the physics of inflation. research topic that no one had ever done before, but he followed the three steps: theory, measurement and application. Congratulations! I am very proud of the fact that we were able to achieve all three steps. Unfortunately, I did not achieve any great breakthrough in detecting new inflation physics, but we have paved the way for future research. We can expect to open up other areas of research using the Subaru Prime Focus spectrograph,” Takada said.
The methods and results of this study will allow future researchers to further test the theory of inflation.
More information:
Toshiki Kurita et al, Constraints on anisotropic primordial non-Gaussianity from intrinsic alignments of SDSS-III BOSS galaxies, Physical examination D (2023). DOI: 10.1103/PhysRevD.108.083533. On arXiv: DOI: 10.48550/arXiv.2302.02925
Provided by the Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo
Quote: Researchers study a million galaxies to discover how the universe began (December 22, 2023) retrieved December 22, 2023 from
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